Seriously, in English "green great dragon" is simply wrong - there's no semantic distinction here. Size before color, so it's "great green dragon." Just in case anyone is wondering "great" has the literal (non metaphorical) meaning "large in size."
A great dragon is distinct from a komodo dragon or, from a eurocentric view, a Chinese dragon. 'A green great dragon' makes perfect sense used in the appropriate context.
"green great dragon" - the dragon is green and happens to be great
"great green dragon" - the greatness of the dragon comes from the fact that it's green